Method and apparatus for measuring a parameter of a vehicle electrical system

ABSTRACT

An automotive vehicle electrical system tester is provided for testing an electrical system having wiring which couple a load to a battery. The automotive vehicle electrical system tester is configured to measure an electrical parameter of the wiring and includes a first battery terminal connection configured to couple to a first terminal of the battery. A test connection is configured to couple to a wire of the electrical system which extends between the first terminal of the battery and the load. Test circuitry coupled to the first battery terminal connection and the test connection is configured to draw current from the battery along a path through the wire and to the test connection. The test circuitry measures an electrical parameter of the wire.

The present application is a Continuation-In-Part of and claims priority of U.S. patent application Ser. No. 11/641,594, filed Dec. 19, 2006, which is a Divisional of U.S. patent application Ser. No. 10/656,526, filed Sep. 5, 2003, now U.S. Pat. No. 7,154,276, the contents of which are hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates to the measurement of electrical parameters of a vehicle electrical system. More specifically, the present invention relates to measuring an electrical parameter of an electrical system of a vehicle using a plurality of connections to the electrical system.

Various types of devices related to battery tester, vehicle diagnostics and the like are described in U.S. Pat. No. 3,873,911, issued Mar. 25, 1975, to Champlin; U.S. Pat. No. 3,909,708, issued Sep. 30, 1975, to Champlin; U.S. Pat. No. 4,816,768, issued Mar. 28, 1989, to Champlin; U.S. Pat. No. 4,825,170, issued Apr. 25, 1989, to Champlin; U.S. Pat. No. 4,881,038, issued Nov. 14, 1989, to Champlin; U.S. Pat. No. 4,912,416, issued Mar. 27, 1990, to Champlin; U.S. Pat. No. 5,140,269, issued Aug. 18, 1992, to Champlin; U.S. Pat. No. 5,343,380, issued Aug. 30, 1994; U.S. Pat. No. 5,572,136, issued Nov. 5, 1996; U.S. Pat. No. 5,574,355, issued Nov. 12, 1996; U.S. Pat. No. 5,583,416, issued Dec. 10, 1996; U.S. Pat. No. 5,585,728, issued Dec. 17, 1996; U.S. Pat. No. 5,589,757, issued Dec. 31, 1996; U.S. Pat. No. 5,592,093, issued Jan. 7, 1997; U.S. Pat. No. 5,598,098, issued Jan. 28, 1997; U.S. Pat. No. 5,656,920, issued Aug. 12, 1997; U.S. Pat. No. 5,757,192, issued May 26, 1998; U.S. Pat. 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No. 10/310,385, filed Dec. 5, 2002, entitled BATTERY TEST MODULE; U.S. Ser. No. 10/653,342, filed Sep. 2, 2003, entitled ELECTRONIC BATTERY TESTER CONFIGURED TO PREDICT A LOAD TEST RESULT; U.S. Ser. No. 10/441,271, filed May 19, 2003, entitled ELECTRONIC BATTERY TESTER; U.S. Ser. No. 09/653,963, filed Sep. 1, 2000, entitled SYSTEM AND METHOD FOR CONTROLLING POWER GENERATION AND STORAGE; U.S. Ser. No. 10/174,110, filed Jun. 18, 2002, entitled DAYTIME RUNNING LIGHT CONTROL USING AN INTELLIGENT POWER MANAGEMENT SYSTEM; U.S. Ser. No. 10/258,441, filed Apr. 9, 2003, entitled CURRENT MEASURING CIRCUIT SUITED FOR BATTERIES; U.S. Ser. No. 10/681,666, filed Oct. 8, 2003, entitled ELECTRONIC BATTERY TESTER WITH PROBE LIGHT; U.S. Ser. No. 10/783,682, filed Feb. 20, 2004, entitled REPLACEABLE CLAMP FOR ELECTRONIC BATTERY TESTER; U.S. Ser. No. 10/791,141, filed Mar. 2, 2004, entitled METHOD AND APPARATUS FOR AUDITING A BATTERY TEST; U.S. Ser. No. 10/867,385, filed Jun. 14, 2004, entitled ENERGY MANAGEMENT SYSTEM FOR AUTOMOTIVE VEHICLE; U.S. Ser. No. 10/896,834, filed Jul. 22, 2004, entitled ELECTRONIC BATTERY TESTER; U.S. Ser. No. 10/958,821, filed Oct. 5, 2004, entitled IN-VEHICLE BATTERY MONITOR; U.S. Ser. No. 10/958,812, filed Oct. 5, 2004, entitled SCAN TOOL FOR ELECTRONIC BATTERY TESTER; U.S. Ser. No. 11/008,456, filed Dec. 9, 2004, entitled APPARATUS AND METHOD FOR PREDICTING BATTERY CAPACITY AND FITNESS FOR SERVICE FROM A BATTERY DYNAMIC PARAMETER AND A RECOVERY VOLTAGE DIFFERENTIAL, U.S. Ser. No. 60/587,232, filed Dec. 14, 2004, entitled CELLTRON ULTRA, U.S. Ser. No. 11/018,785, filed Dec. 21, 2004, entitled WIRELESS BATTERY MONITOR; U.S. Ser. No. 60/653,537, filed Feb. 16, 2005, entitled CUSTOMER MANAGED WARRANTY CODE; U.S. Ser. No. 11/063,247, filed Feb. 22, 2005, entitled ELECTRONIC BATTERY TESTER OR CHARGER WITH DATABUS CONNECTION; U.S. Ser. No. 60/665,070, filed Mar. 24, 2005, entitled OHMMETER PROTECTION CIRCUIT; U.S. Ser. No. 11/141,234, filed May 31, 2005, entitled BATTERY TESTER CAPABLE OF IDENTIFYING FAULTY BATTERY POST ADAPTERS; U.S. Ser. No. 11/143,828, filed Jun. 2, 2005, entitled BATTERY TEST MODULE; U.S. Ser. No. 11/146,608, filed Jun. 7, 2005, entitled SCAN TOOL FOR ELECTRONIC BATTERY TESTER; U.S. Ser. No. 60,694,199, filed Jun. 27, 2005, entitled GEL BATTERY CONDUCTANCE COMPENSATION; U.S. Ser. No. 11/178,550, filed Jul. 11, 2005, entitled WIRELESS BATTERY TESTER/CHARGER; U.S. Ser. No. 60/705,389, filed Aug. 4, 2005, entitled PORTABLE TOOL THEFT PREVENTION SYSTEM, U.S. Ser. No. 11/207,419, filed Aug. 19, 2005, entitled SYSTEM FOR AUTOMATICALLY GATHERING BATTERY INFORMATION FOR USE DURING BATTERY TESTER/CHARGING, U.S. Ser. No. 60/712,322, filed Aug. 29, 2005, entitled AUTOMOTIVE VEHICLE ELECTRICAL SYSTEM DIAGNOSTIC DEVICE, U.S. Ser. No. 60/713,168, filed Aug. 31, 2005, entitled LOAD TESTER SIMULATION WITH DISCHARGE COMPENSATION, U.S. Ser. No. 60/731,881, filed Oct. 31, 2005, entitled PLUG-IN FEATURES FOR BATTERY TESTERS; U.S. Ser. No. 60/731,887, filed Oct. 31, 2005, entitled AUTOMOTIVE VEHICLE ELECTRICAL SYSTEM DIAGNOSTIC DEVICE; U.S. Ser. No. 11/304,004, filed Dec. 14, 2005, entitled BATTERY TESTER THAT CALCULATES ITS OWN REFERENCE VALUES; U.S. Ser. No. 60/751,853, filed Dec. 20, 2005, entitled BATTERY MONITORING SYSTEM; U.S. Ser. No. 11/304,004, filed Dec. 14, 2005, entitled BATTERY TESTER WITH CALCULATES ITS OWN REFERENCE VALUES; U.S. Ser. No. 60/751,853, filed Dec. 20, 2005, entitled BATTERY MONITORING SYSTEM; U.S. Ser. No. 11/356,299, filed Feb. 16, 2006, entitled CENTRALLY MONITORED SALES OF STORAGE BATTERIES; U.S. Ser. No. 11/356,443, filed Feb. 16, 2006, entitled ELECTRONIC BATTERY TESTER WITH NETWORK COMMUNICATION; U.S. Ser. No. 11/498,703, filed Aug. 3, 2006, entitled THEFT PREVENTION DEVICE FOR AUTOMOTIVE VEHICLE SERVICE CENTERS; U.S. Ser. No. 11/507,157, filed Aug. 21, 2006, entitled APPARATUS AND METHOD FOR SIMULATING A BATTERY TESTER WITH A FIXED RESISTANCE LOAD; U.S. Ser. No. 11/511,872, filed Aug. 29, 2006, entitled AUTOMOTIVE VEHICLE ELECTRICAL SYSTEM DIAGNOSTIC DEVICE; U.S. Ser. No. 11/519,481, filed Sep. 12, 2006, entitled BROAD-BAND LOW-CONDUCTANCE CABLES FOR MAKING KELVIN CONNECTIONS TO ELECTROCHEMICAL CELLS AND BATTERIES; U.S. Ser. No. 60/847,064, filed Sep. 25, 2006, entitled STATIONARY BATTERY MONITORING ALGORITHMS; U.S. Ser. No. 11/638,771, filed Dec. 14, 2006, entitled BATTERY MONITORING SYSTEM; U.S. Ser. No. 11/641,594, filed Dec. 19, 2006, entitled METHOD AND APPARATUS FOR MEASURING A PARAMETER OF A VEHICLE ELECTRONIC SYSTEM; U.S. Ser. No. 11/711,356, filed Feb. 27, 2007, entitled BATTERY TESTER WITH PROMOTION FEATURE; U.S. Ser. No. 11/811,528, filed Jun. 11, 2007, entitled ALTERNATOR TESTER; U.S. Ser. No. 60/950,182, filed Jul. 17, 2007, entitled BATTERY TESTER FOR HYBRID VEHICLE; U.S. Ser. No. 60/973,879, filed Sep. 20, 2007, entitled ELECTRONIC BATTERY TESTER FOR TESTING STATIONARY BATTERIES; U.S. Ser. No. 11/931,907, filed Oct. 31, 2007, entitled BATTERY MAINTENANCE WITH PROBE LIGHT; U.S. Ser. No. 60/992,798, filed Dec. 6, 2007, entitled STORAGE BATTERY AND BATTERY TESTER; U.S. Ser. No. 12/099,826, filed Apr. 9, 2008, entitled BATTERY RUN DOWN INDICATOR; U.S. Ser. No. 61/061,848, filed Jun. 16, 2008, entitled KELVIN CLAMP FOR ELECTRONICALLY COUPLING TO A BATTERY CONTACT; U.S. Ser. No. 12/168,264, filed Jul. 7, 2008, entitled BATTERY TESTERS WITH SECONDARY FUNCTIONALITY; U.S. Ser. No. 12/174,894, filed Jul. 17, 2008, entitled BATTERY TESTER FOR ELECTRIC VEHICLE; which are incorporated herein in their entirety.

There is an ongoing need to measure parameters of electrical systems of vehicles and heavy equipment. Such measurements can be used to diagnose operation, failure or impending failure of components or subsystems of electrical systems. For example, in electrical systems used in vehicles, measurement of electrical parameters of such systems can be used to diagnose operation of the system or indicate that maintenance is required before ultimate failure.

One particular measurement is the resistance of cabling used in the vehicle. For example, one such cable or set of cables connects the battery the of vehicle to the starter motor. The starter motor has a relatively large current draw and even a relatively small cable resistance can have a significant impact on operation of the starter motor.

Because the cable resistance is relatively small it typically cannot be measured using a standard ohm meter or other techniques which are normally used to measure resistance. One technique which has been used to measure the cable resistance is to run a very large current through the cable and measure the voltage drop. However, this is cumbersome and requires components capable of handling the large current.

SUMMARY OF THE INVENTION

An automotive vehicle electrical system tester is provided for testing an electrical system having wiring which couple a load to a battery. The automotive vehicle electrical system tester is configured to measure an electrical parameter of the wiring and includes a first battery terminal connection configured to couple to a first terminal of the battery. A test connection is configured to couple to a wire of the electrical system which extends between the first terminal of the battery and the load. Test circuitry coupled to the first battery terminal connection and the test connection is configured to draw current from the battery along a path through the wire and to the test connection. The test circuitry measures an electrical parameter of the wire.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram of an electrical system of a vehicle.

FIG. 2 is a simplified block diagram showing an automotive vehicle electrical system tester in accordance with one example embodiment of the present invention.

FIG. 3A is a simplified electrical diagram showing a configuration of circuitry for measuring a parameter of a wire of the vehicle.

FIG. 3B is a simplified electrical diagram showing a configuration of circuitry for testing another wire of the vehicle.

FIG. 4 is a simplified block diagram showing sense circuitry for use with the tester of FIG. 2.

FIG. 5 is simplified block diagram showing current circuitry for use with the electrical system tester of FIG. 2.

FIG. 6 is a front plan view of the electrical system tester of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a simplified diagram of an electrical system 10 of a vehicle 12. Electrical system 10 includes a battery 20, a load 22 and cables 24 and 26 which connect load 22 to the positive terminal 30 of battery 20 and the negative terminal 32 of battery 20, respectively. Cables 24 and 26 are illustrated as having resistances R₁ and R₂, respectively.

FIG. 1 also shows Kelvin connections 40 and 42 coupled to the positive terminal 30 and the negative terminal 32 of battery 20 respectively.

Kelvin connection 40 has a sense connection K1 _(S) and a current connection K1 _(C). Similarly, Kelvin connection 42 has a sense connection K2 _(S) and a current connection K2 _(C). FIG. 1 also illustrates test connections 44 and 46. In the embodiment of FIG. 1, these are illustrated as being Kelvin connections, however the present invention is not limited to this arrangement. Test connection 44 is connected between load 22 and cable 24. Similarly, test connection 46 is connected between load 22 and cable 26. Test connection 44 includes a sense connection T1 _(S) and a current connection T1 _(C). Test connection 46 includes a sense connection T2 _(S) and a current connection T2 _(C).

As discussed in the Background section, the resistances R₁ and R₂ of cables 24 or 26 can impact the amount of power which can be delivered to load 22. Even if the resistance values are relatively small, if a relatively large current passes through cables 24 and 26, the resultant voltage drop can significantly reduce the voltage across load 22 and therefore the amount of power which can be delivered to load 22. In many instances, it is desirable to measure the resistance R₁ and R₂ of cables 24 and 26, respectively, in order to identify a cable with a resistance which is too high. One technique which has been used to measure the resistance of the cables is to pass a large current through the cable and measure the resulting voltage drop across the cable. However, this is a cumbersome test and requires electrical test equipment which is capable of handling the large current draw. The present invention provides an apparatus and technique for measuring the resistance of a cable in a configuration similar to that shown in FIG. 1.

FIG. 2 is a simplified block diagram of automotive vehicle electrical system tester 100 in accordance with one example embodiment of the present invention. Tester 100 includes sense circuitry 102 which couples to connections K1 _(S), K2 _(S), T1 _(S) and T2 _(S). Similarly, tester 100 includes current drive circuitry 104 which connects to K1 _(C), K2 _(C), T1 _(C) and T2 _(C). Power supply circuitry 106 also couples to K1 _(C) and K2 _(C) and provides a power output which may be used for powering electrical components of tester 100. In another example embodiment, tester 100 includes a separate power source such as an internal battery. A microprocessor 108 couples to sense circuitry 102 and current circuitry 104 and operates in accordance with instructions stored in a memory 110. Memory 110 can include both volatile and non-volatile memory and may be used for permanently or temporarily storing information. User input/output circuitry 112 is shown coupled to microprocessor 108 and may includes for example, button inputs, a display for output, audio inputs and outputs, etc. Such audio inputs or outputs can include a voice output or input, alarms, beepers, buzzers, etc. FIG. 2 also illustrates I/O circuitry 114 which can be optionally used by microprocessor 108 to communicate with any other type of device including network communications, other diagnostic components, centralized locations, printers, etc. In one example configuration, this includes a connection for coupling to the databus of the vehicle 12. For example, this could be an OBD II type databus.

The load 22 of the vehicle can be any type of load including loads which draw high current levels, for example, a starter motor, a magnetic switch, a ground connection, wiring harness, a terminal which may be susceptible to corrosion, a connection through a bolt which may have inappropriate torque or otherwise provide a poor connection, data carrying wires, sensor wiring, trailer wiring, etc. The invention is applicable to all wire sizes including small, medium and large gauge and is not limited to those discussed herein. In one example embodiment, the output is related to a particular current draw through the cabling. For example, the output can comprise an indication that there is a 0.5 volt drop through the cable when carrying a 500 amp current. Such parameter can also be used, for example, in a pass/fail test, i.e., if the voltage drop is more than a particular threshold at a given current level, a failure indication can be provided as an output. In one embodiment, the measured parameters comprise dynamic parameters such as dynamic conductance. However, any dynamic parameter can be used in accordance with the present invention including dynamic resistance, reactance, impedance, conductance, susceptance, and/or admittance, including any combination of these parameters, or others.

FIG. 3A is a simplified block diagram showing the electrical connections to wiring 24 for measurement of resistance R₁. As illustrated in FIG. 3A, a current I_(L) is applied by current force 104 through resistance R₁ of cable 24. The current I_(L) flows through a current path from the positive terminal 30 of battery 20, through cable 24 and resistance R₁, and into test connector current connection T1 _(C) of test connector 44. The current source 104 provides a path for current from T1 _(C) to the K2 _(C) connection of Kelvin connector 42. This, as illustrated in FIG. 3A, couples to the negative terminal 32 of battery 20. The current source 104 can be an active or passive current source. For example, current source 104 may be a resistive load which operates under the control of microprocessor 108. Sense circuitry 102 is coupled across resistance R₁ using the K1 _(S) sense connection of Kelvin connector 40 and the T1 _(S) sense connection of test connector 44. Note that as discussed herein, the test connections 44 and 46 are illustrated as Kelvin connections, however the invention is not limited to this configuration.

FIG. 3B is a simplified block diagram showing a similar arrangement used to measure the resistance R₂ of cable 26. In FIG. 3B, a current I_(L) is applied to resistance R₂ using current source 104 along with connection K1 _(C) of Kelvin connector 40 which couples to the positive terminal 30 of battery 20 and test connection T2 _(C) of test connector 46. A sense connection for sense circuitry 102 is provided by connector K2 _(S) of Kelvin connector 42 coupled to the negative terminal 32 of battery 20 along with the connector T2 _(S) of test connector 46.

FIG. 4 is simplified diagram showing one example configuration of sense circuitry 102. As illustrated in FIG. 4, sense circuitry 102 includes a multiplexor 150 operated under the control of microprocessor 108 which couples to the Kelvin sense connections K1 _(S) and K2 _(S). Multiplexor 150 is used to selectively couple one of the sense connections K1 _(S) and K2 _(S) to a differential amplifier 154. Similarly, a second multiplexor 152 operates under the control of microprocessor 108 and operates to selectively couple of the test sense connections T1 _(S) and T2 _(S) to the differential amplifier 154. Differential amplifier provides an amplified differential output to an analog to digital converter 156 which digitizes the analog signal and provides a digital signal to microprocessor 108. In one example configuration, the gain of the differential amplifier 154 maybe adjusted by microprocessor 108 to selectively increase or decrease the sensitivity of the circuitry.

FIG. 5 is a simplified block diagram showing one example embodiment of current circuitry 104 in greater detail. An embodiment illustrated in FIG. 5, a multiplexor 160 operates under the control of microprocessor 104 and selectively couples Kelvin connection K1 _(C) of Kelvin connector 40 or Kelvin connection K2 _(C) of Kelvin connector 42 to a current source 164. Similarly, a multiplexor 162 operates under the control of microprocessor 108 and selectively couples test current connection T1 _(C) of test connector 44 or test current connection T2 _(C) of test connector 46 to the current source 164. Current source 164 is coupled to microprocessor 108 and is controlled by microprocessor 108. Current source 164 may comprise, for example, a fixed resistance (in which case it is not necessary to connect current source 164 to microprocessor 108) or a plurality of selectable resistors or a variable resistance which provides a current path between one of the selected connectors coupled to multiplexor 160 and one of the connectors selected by multiplexor 162. In this configuration, the current source 164 is a passive current source formed by a resistance. However, an active current source may also be employed. Current 164 may also include current sense circuitry which is configured to measure a current I_(C) flowing there through. This information can be provided to microprocessor 108 for use in determining the resistance of resistor R₁ or R₂ of cables 24 or 26, respectively.

During operation, microprocessor 108 shown in FIG. 2 controls operation of multiplexors 150, 152, 160 and 162 to arrange the test circuitry in the configuration illustrated in FIGS. 3A and 3B. The resistance being measured (R1 or R2) is calculated by microprocessor 108 using Ohms' law R=V/I where R is the resistance being measured, V is the voltage sensed by sense circuitry 102 and I is the current flowing through current circuitry 104. Operation by microprocessor 108 may be controlled by user I/O 112 shown in FIG. 2. For example, an operator may instruct the microprocessor 108 to initiate a measurement. In another example configuration, the operator instructs the microprocessor as to the amount of current I_(C) to be applied during the test. This can be selected by the user, for example, based upon the type of wiring being measured, the specific use for the particular wiring being measured, the gauge of the wiring being measured, or other considerations as desired. The microprocessor 108 can provide an output, such as a pass/fail output by comparing the measured values with threshold levels. These threshold levels can be measured by a user through user I/O 112 and/or stored in memory 110. The particular thresholds may be changed based upon the particular test criteria being used. As discussed above, this could be based upon the particular wiring or cabling type, the use of which the wiring is applied, the gauge of the wiring, etc. Microprocessor 108 can also be configured to provide other information to the operator. For example, this includes any information which may be measured or otherwise retrieved by microprocessor 108 including voltage measures, maximum or minimum measurements, signal wave forms, user instructions or prompts, etc. In one example configuration, user I/O 112 may include an audible output such as voice prompting or verbal test results, or other sounds to instruct or provide information to an operator.

In one configuration, the user I/O 112 is used by an operator to instruct the microprocessor 108 as to the particular circuit configuration to be used as illustrated in FIGS. 3A and 3B. In another example configuration, for example, if a single test connector 44 or 46 is employed, microprocessor 108 measures a voltage using sense circuitry 102 between the test connection and Kelvin connectors 40 and/or 42. This measured voltage is used by microprocessor 108 to determine whether the test connector is coupled as showing by test connector 44 shown in FIG. 1 or if the test connector is coupled as shown by test connector 46 shown in FIG. 1. Based upon the measured voltage, microprocessor configures the circuitry in the proper configuration as illustrated in FIG. 3A or 3B.

FIG. 6 is a plan view showing tester 100 which includes a housing 200 carrying a display 202 and user input buttons 204, 206 and 208. Display 202 and buttons 204-208 can comprise user I/O 112 shown in FIG. 2. Another example component of the user input/output 112 includes LED's 210A, 210B and 212A and 212B. A battery cable 220 couples to housing 200 to plug 222 and connects to Kelvin connectors 40 and 42 shown in FIG. 1. The Kelvin connectors 40 and 42 can comprise, for example, “alligator” type clamps for coupling to the terminals of battery 20. A test cable 230 couples to housing 200 to plug 232. In the example shown in FIG. 6, a distal end of test cable 230 comprises a piercing probe 242 configured to pierce through an insulation of a cable under test. Note that in such a configuration, the test connector, such as 44 or 46, may or may not be a Kelvin connection as illustrated in the above figures and may comprise a single connector. Some loss in accuracy may be expected however in some situations this may be acceptable. In another example configuration, the Kelvin connectors are provided through test cable 230 up to the distal end 240 of the test cable 230. At the distal end 240, the two Kelvin connectors are coupled together and a single connection is used for connecting to the cable under test. In yet another example configuration, the piercing probe 242 comprises two piercing probes such that a Kelvin connection is provided by piercing through the insulation of the cable. A piercing probe is not necessary and any type of test connection may be used including standard test probe configuration such as those available on volt meters, clamps, etc.

Button 204 can be configured as a “enter” button and buttons 206 and 208 can be configured as “up” and “down” buttons for scrolling through and selecting menu items displayed on display 208. For example, this can be used to also to receive information regarding the “gauge” of the wire under test. LED's 210 and 212A and 212B can be used to display test information. For example, when a wire of a positive polarity is detected either or both LED's 212 or 212B may be illuminated. Similarly, when test probe 242 is connected is wired to a wire of negative polarity, either or both of the LED 210A/210B may be illuminated. Button 204 can be used for initiate test button and cause the test to begin. Upon completion of the test, the microprocessor 108 can be configured to illuminate LED 210B or 212B if the test is successful. If the wire fails the test, LED 210A or 212B may be illuminated. In a similar configuration, an audio output can be provided, for example, a high pitch solid continuous tone to indicate a “good” wire, a “good” power wire, a high pitch beeping tone to indicate a “bad” power wire, a low pitch solid tone to indicate a “good” ground wire, and a low beeping tone to indicate a “bad” ground wire.

In another example configuration, a wire size gauge 250 is provided on the side of housing 200. In this example, the wire size gauge 250 provides three wire size gauges, 252A, 252B and 252C. These may be used by an operator to determine the gauge of the wire under test and input into the microprocessor 108 using user I/O 112. In another example configuration, wire size gauge 250 comprises an automatic gauge in which the wire under test is placed into a slot or the like and a sensor automatically determines the gauge of the wire and provides this information to microprocessor 108.

In one example configuration, a small gauge wire is tested with a current load of 1.25 amps, a medium gauge wire is tested with a current load of 2.5 amps, and a large gauge wire is tested with a current load of 5.0 amps, all with a fixed failure threshold of 0.2 volts. (i.e., if the measured voltage across the wire is greater than 0.2 volts, a failure is indicated). In another example embodiment, a fixed current load is provided and microprocessor 108 scales the measured result based upon the gauge of the wire.

Although the above description shows two different Kelvin connections to the battery terminals, in one configuration, Kelvin connections are not used and another example configuration, only a single Kelvin connection is used or no Kelvin connections are used. Similarly, only a single test connector may be employed and the invention does not require the two test connectors described above. Such an embodiment may be employed if desired, for example, to simultaneously measure the resistances of two separate wires. In a typical configuration, a single test connector will be employed. Similarly, the test connector may be a single connector and a Kelvin connection is not required. If a Kelvin connection is used, the Kelvin connection point can be configured anywhere along the test connector wiring and may be at a point that the test connector couples to the wiring of the vehicle, or at some other point in the wiring between the distal end of the test connector and the circuitry of the tester. The measurements may be made using static measurement techniques to obtain a static parameter or may be made using dynamic measurement techniques to obtain a dynamic parameter. Although the discussion above has generally referred to “resistance”, the present invention is not limited to resistance and the parameter measured may be any parameter of the wire including those which have frequency dependent components. The tester may be powered with power from the battery of the electrical system or may contain an independent power source, for example, an internal battery. As discussed above, in some embodiments, Kelvin connections are provided to the terminals of the battery. In such a configuration, a parameter of the battery may be measured using the techniques discussed in the Background section, or other techniques.

The connection tip may be interchangeable and may be comprised a test probe, piercing tip, connector coupled to a particular type of electrical connection on the vehicle, or other configurations. As these tips are interchangeable, the overall resistance of the test connection may vary. Thus, in some configurations, the microprocessor 108 can be configured to implement a zeroing function whereby an operator can calibrate the measurement for the resistance of the wire based upon the selected probe tip. Such a configuration would typically not be required for a Kelvin connection. The zeroing function can be performed automatically by the microprocessor by measuring the resistance through the electrical connection, can be entered manually by an operator, may be selected by an operator scrolling through a table and selecting the probe in use. In such a configuration, memory 110 shown in FIG. 2 can contain information related to the resistance value for a particular probe.

In one configuration the measurement is presented to the operator in the form of “voltage drop at XX amps”. However, the actual measurement may be performed at a current level other than that presented to the operator. If a small current is employed, conductance measurement techniques can be used to determine the voltage drop. If a current other than the displayed current is employed, the microprocessor 180 performs a scaling on the measurement. For example, if 5 amps is used to perform the measurement, the microprocessor 108 can compute the results in voltage drops at a different value such as 25 amps for display to the operator. This scaling can occur automatically, or can be selected by an operator. Such selection may be, for example, by scrolling through a utility menu presented to the operator using user I/O 110. In such a configuration, memory 110 can contain a scaling factor for use by the microprocessor 108.

In one embodiment, a relatively small current is employed. This reduces the amount of heat generated and reduces the power requirements of the testing device. The measurement can be performed using a dynamic forcing function such as a time varying current signal. For example, short pulses can be used if the device is not capable of sustaining a large current output for an extended period of time. In one example, a pulse width between 10 and 100 msec is used to perform the measurement.

The microprocessor can be configured to automatically sense the polarity of the connection. In such a configuration, the microprocessor sense the voltage measured and determines whether the probe is coupled to a power wire or to a ground wire and the appropriate load is applied. For example, if zero volts is sensed, the wire being tested is most likely a ground wire. Similar, if twelve volts is sensed, the wire being tested is most likely used to supply power. However, in some example configurations, a zero voltage reading may also indicate that the wire being tested is not connected. Similarly, a twelve volt reading may not be a power supplying wire if, for example, the alternator of the vehicle is generating a fifteen volt output. One example configuration to address this concern is to bias the probe tip to a voltage level. For example, circuitry within component 104 (or 102) can be provided to bias the probe tip to a value somewhere between the voltage at the two power leads coupled to the battery 20. When the probe tip is then coupled to the vehicle, the voltage at the probe tip will be pulled to either a more negative or positive value. Microprocessor 108 can sense this voltage and make a determination as to whether the probe is connected to a power lead or a ground lead. For example, if the probe tip voltage is within a predetermined voltage level from electrical ground, microprocessor can determine that the probe is connected to a ground connection. Similarly, if the probe tip is pulled within a predetermined voltage level from the plus connection of the battery, a microprocessor 108 can determine that a power lead is under test. In one example, the predetermined voltage is one volt which is advantageous if a protective diode is employed in the lead which would provide a voltage drop of 0.6 volts.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. The measurements can be taken using multiple connections to the electrical system or by moving a single pair of connections to various positions on the electrical system. An output can be provided to instruct the operator where to place the connections. 

1. A vehicle electrical system tester for testing the electrical system of a vehicle, the electrical system having wiring which couples a load to a battery, the vehicle electrical system tester configured to measure an electrical parameter of the wiring and comprising: a first battery terminal connection configured to couple to a first terminal of the battery; a second battery terminal connection configured to couple to a second terminal of the battery; a test connection configured to couple to a wire of the electrical system which is electrically connected between the first or second terminal of the battery and the load; and test circuitry coupled to the first and second battery terminal connections and the test connection configured to draw current from the battery along a path through the wire and the test connection and return the current to the battery, and measure the electrical parameter of the wire with a sensor coupled to the test connection.
 2. The apparatus of claim 1 wherein the first battery terminal connection comprises a Kelvin connection.
 3. The apparatus of claim 1 wherein the first and second battery terminal connections comprise Kelvin connections.
 4. The apparatus of claim 1 wherein the test circuitry is powered with power from the first and second battery terminal connections.
 5. The apparatus of claim 1 wherein the test connection comprises a Kelvin connection.
 6. The apparatus of claim 1 wherein the test connection comprises a piercing probe configured to pierce insulation of the wire.
 7. The apparatus of claim 1 wherein the test circuitry includes an adjustable load configured to adjust the current through the wire.
 8. The apparatus of claim 1 including a display coupled to the test circuitry.
 9. The apparatus of claim 1 including a user input coupled to the test circuitry.
 10. The apparatus of claim 9 when the user input is configured to receive information related to a gauge of the wire.
 11. The apparatus of claim 1 wherein the test circuitry is configured to control the current through the wire based upon a connection of the wire to the positive terminal of the battery or a connection of the wire to a negative terminal of the battery.
 12. The apparatus of claim 1 further including a housing and wherein the housing includes a wire gauge.
 13. The apparatus of claim 1 including an audio output coupled to the test circuitry.
 14. The apparatus of claim 13 wherein the audio output comprises a voice output.
 15. The apparatus of claim 1 wherein the test circuitry provides an output in the form of “voltage drop at XX amps” and wherein current drawn by the test circuitry has a value which is different than XX amps.
 16. The apparatus of claim 1 wherein the test circuitry provides an output related to electrical parameter of the wire and a scaling factor.
 17. The apparatus of claim 1 wherein the electrical parameter of the wire comprises a dynamic parameter
 18. The apparatus of claim 1 wherein the test circuitry is configured to identify the wire as comprising a ground wire or a power wire.
 19. The apparatus of claim 18 wherein the test connection is biased to a voltage level which is between a first battery terminal voltage and a second battery terminal voltage.
 20. The apparatus of claim 1 wherein the test circuitry includes a zeroing function configured to compensate for resistance of the test connection.
 21. A method of testing wiring an electrical system of a vehicle, the wiring extending between a load and a battery, the method comprising: coupling to a first battery terminal of the battery with a first battery terminal connection; coupling to a second battery terminal of the battery with a second battery terminal connection; coupling a test connection to a wire of the vehicle which electrically couples to the load; applying a current through the wire between the battery and the test connection; and sensing a voltage drop across the wire between the battery and the test connection.
 22. The method of claim 21 wherein the first battery terminal connection comprises a Kelvin connection.
 23. The method of claim 21 wherein the first and second battery terminal connections comprise Kelvin connections.
 24. The method of claim 21 including powering test circuitry with power from the first and second battery terminal connections.
 25. The method of claim 21 wherein the test connection comprises a Kelvin connection.
 26. The method of claim 21 wherein the test connection comprises a piercing probe configured to pierce insulation of the wire.
 27. The method of claim 21 including providing an adjustable load configured to adjust the current through the wire.
 28. The method of claim 21 including displaying information based upon the sensed voltage drop.
 29. The method of claim 21 including receiving a user input.
 30. The method of claim 29 when the user input is related to a gauge of the wire.
 31. The method of claim 21 including controlling the current through the wire based upon a connection of the wire to the positive terminal of the battery or a connection of the wire to a negative terminal of the battery.
 32. The method of claim 21 including providing a housing and wherein the housing includes a wire gauge.
 33. The method of claim 21 including providing an audio output based upon the sensed voltage circuitry.
 34. The method of claim 33 wherein the audio output comprises a voice output. 